Linux文本处理指令xargs-man帮助手册

发布时间:2024年01月23日

Linux文本处理指令xargs-man帮助手册

XARGS(1)                           General Commands Manual                          XARGS(1)

NAME
       xargs - build and execute command lines from standard input

SYNOPSIS
       xargs [options] [command [initial-arguments]]

DESCRIPTION
       This  manual  page  documents  the  GNU version of xargs.  xargs reads items from the
       standard input, delimited by blanks (which can be protected  with  double  or  single
       quotes  or  a backslash) or newlines, and executes the command (default is /bin/echo)
       one or more times with any initial-arguments followed by items read from standard in‐
       put.  Blank lines on the standard input are ignored.

       The command line for command is built up until it reaches a system-defined limit (un‐
       less the -n and -L options are used).  The specified command will be invoked as  many
       times as necessary to use up the list of input items.  In general, there will be many
       fewer invocations of command than there were items in the input.  This will  normally
       have  significant  performance  benefits.   Some commands can usefully be executed in
       parallel too; see the -P option.

       Because Unix filenames can contain blanks and newlines, this default behaviour is of‐
       ten  problematic;  filenames  containing  blanks and/or newlines are incorrectly pro‐
       cessed by xargs.  In these situations it is better to use the -0 option,  which  pre‐
       vents  such  problems.   When using this option you will need to ensure that the pro‐
       gram which produces the input for xargs also uses a null character  as  a  separator.
       If that program is GNU find for example, the -print0 option does this for you.

       If  any invocation of the command exits with a status of 255, xargs will stop immedi‐
       ately without reading any further input.  An error message is issued on  stderr  when
       this happens.

OPTIONS
       -0, --null
              Input  items  are terminated by a null character instead of by whitespace, and
              the quotes and backslash are not special (every character is taken literally).
              Disables  the  end  of  file string, which is treated like any other argument.
              Useful when input items might contain white space, quote marks, or  backslash‐
              es.  The GNU find -print0 option produces input suitable for this mode.

       -a file, --arg-file=file
              Read items from file instead of standard input.  If you use this option, stdin
              remains unchanged when commands are run.  Otherwise, stdin is redirected  from
              /dev/null.

       --delimiter=delim, -d delim
              Input  items  are terminated by the specified character.  The specified delim‐
              iter may be a single character, a C-style character escape such as \n,  or  an
              octal  or hexadecimal escape code.  Octal and hexadecimal escape codes are un‐
              derstood as for the printf command.   Multibyte characters are not  supported.
              When processing the input, quotes and backslash are not special; every charac‐
              ter in the input is taken literally.  The -d option disables  any  end-of-file
              string,  which  is  treated  like any other argument.  You can use this option
              when the input consists of simply newline-separated items, although it is  al‐
              most  always  better to design your program to use --null where this is possi‐
              ble.

       -E eof-str
              Set the end of file string to eof-str.  If the end of file string occurs as  a
              line  of  input,  the  rest  of the input is ignored.  If neither -E nor -e is
              used, no end of file string is used.

       -e[eof-str], --eof[=eof-str]
              This option is a synonym for the -E option.  Use -E  instead,  because  it  is
              POSIX  compliant while this option is not.  If eof-str is omitted, there is no
              end of file string.  If neither -E nor -e is used, no end of  file  string  is
              used.

       -I replace-str
              Replace  occurrences  of  replace-str in the initial-arguments with names read
              from standard input.  Also, unquoted blanks do not terminate input items;  in‐
              stead the separator is the newline character.  Implies -x and -L 1.

       -i[replace-str], --replace[=replace-str]
              This  option  is  a synonym for -Ireplace-str if replace-str is specified.  If
              the replace-str argument is missing, the effect is the same as -I{}.  This op‐
              tion is deprecated; use -I instead.

       -L max-lines
              Use  at most max-lines nonblank input lines per command line.  Trailing blanks
              cause an input line to be logically continued on the next input line.  Implies
              -x.

       -l[max-lines], --max-lines[=max-lines]
              Synonym for the -L option.  Unlike -L, the max-lines argument is optional.  If
              max-lines is not specified, it defaults to one.  The -l option  is  deprecated
              since the POSIX standard specifies -L instead.

       -n max-args, --max-args=max-args
              Use  at  most  max-args arguments per command line.  Fewer than max-args argu‐
              ments will be used if the size (see the -s option) is exceeded, unless the  -x
              option is given, in which case xargs will exit.

       -P max-procs, --max-procs=max-procs
              Run up to max-procs processes at a time; the default is 1.  If max-procs is 0,
              xargs will run as many processes as possible at a time.  Use the -n option  or
              the  -L option with -P; otherwise chances are that only one exec will be done.
              While xargs is running, you can send its process a SIGUSR1 signal to  increase
              the  number  of  commands  to run simultaneously, or a SIGUSR2 to decrease the
              number.  You cannot increase it above an implementation-defined  limit  (which
              is  shown  with  --show-limits).  You cannot decrease it below 1.  xargs never
              terminates its commands; when asked to decrease, it merely waits for more than
              one existing command to terminate before starting another.

              Please  note that it is up to the called processes to properly manage parallel
              access to shared resources.  For example, if more than one of  them  tries  to
              print  to  stdout,  the output will be produced in an indeterminate order (and
              very likely mixed up) unless the processes collaborate in some way to  prevent
              this.   Using some kind of locking scheme is one way to prevent such problems.
              In general, using a locking scheme will help ensure correct output but  reduce
              performance.  If you don't want to tolerate the performance difference, simply
              arrange for each process to produce a separate output file (or  otherwise  use
              separate resources).

       -o, --open-tty
              Reopen  stdin  as  /dev/tty in the child process before executing the command.
              This is useful if you want xargs to run an interactive application.

       -p, --interactive
              Prompt the user about whether to run each command line and read  a  line  from
              the  terminal.   Only  run the command line if the response starts with `y' or
              `Y'.  Implies -t.

       --process-slot-var=name
              Set the environment variable name to a unique  value  in  each  running  child
              process.   Values are reused once child processes exit.  This can be used in a
              rudimentary load distribution scheme, for example.

       -r, --no-run-if-empty
              If the standard input does not contain any nonblanks, do not run the  command.
              Normally, the command is run once even if there is no input.  This option is a
              GNU extension.

       -s max-chars, --max-chars=max-chars
              Use at most max-chars characters per command line, including the  command  and
              initial-arguments  and  the  terminating  nulls  at  the  ends of the argument
              strings.  The largest allowed value is system-dependent, and is calculated  as
              the  argument  length  limit for exec, less the size of your environment, less
              2048 bytes of headroom.  If this value is more than 128KiB, 128Kib is used  as
              the  default value; otherwise, the default value is the maximum.  1KiB is 1024
              bytes.  xargs automatically adapts to tighter constraints.

       --show-limits
              Display the limits on the command-line length which are imposed by the operat‐
              ing  system,  xargs'  choice of buffer size and the -s option.  Pipe the input
              from /dev/null (and perhaps specify --no-run-if-empty) if you don't want xargs
              to do anything.

       -t, --verbose
              Print the command line on the standard error output before executing it.

       -x, --exit
              Exit if the size (see the -s option) is exceeded.

       --help Print a summary of the options to xargs and exit.

       --version
              Print the version number of xargs and exit.

       The options --max-lines (-L, -l), --replace (-I, -i) and --max-args (-n) are mutually
       exclusive. If some of them are specified at the same time, then xargs will  generally
       use  the  option specified last on the command line, i.e., it will reset the value of
       the offending option (given before) to its default value.  Additionally,  xargs  will
       issue a warning diagnostic on stderr.  The exception to this rule is that the special
       max-args value 1 ('-n1') is ignored after the --replace option and its aliases -I and
       -i, because it would not actually conflict.

EXAMPLES
       find /tmp -name core -type f -print | xargs /bin/rm -f

       Find files named core in or below the directory /tmp and delete them.  Note that this
       will work incorrectly if there are any filenames containing newlines or spaces.

       find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f

       Find files named core in or below the directory  /tmp  and  delete  them,  processing
       filenames  in  such  a way that file or directory names containing spaces or newlines
       are correctly handled.

       find /tmp -depth -name core -type f -delete

       Find files named core in or below the directory /tmp and delete them, but more  effi‐
       ciently  than  in  the previous example (because we avoid the need to use fork(2) and
       exec(2) to launch rm and we don't need the extra xargs process).

       cut -d: -f1 < /etc/passwd | sort | xargs echo

       Generates a compact listing of all the users on the system.

EXIT STATUS
       xargs exits with the following status:

              0      if it succeeds

              123    if any invocation of the command exited with status 1-125

              124    if the command exited with status 255

              125    if the command is killed by a signal

              126    if the command cannot be run

              127    if the command is not found

              1      if some other error occurred.

       Exit codes greater than 128 are used by the shell to indicate that a program died due
       to a fatal signal.

STANDARDS CONFORMANCE
       As  of GNU xargs version 4.2.9, the default behaviour of xargs is not to have a logi‐
       cal end-of-file marker.  POSIX (IEEE Std 1003.1, 2004 Edition) allows this.

       The -l and -i options appear in the 1997 version of the POSIX standard,  but  do  not
       appear  in  the 2004 version of the standard.  Therefore you should use -L and -I in‐
       stead, respectively.

       The -o option is an extension to the POSIX standard  for  better  compatibility  with
       BSD.

       The POSIX standard allows implementations to have a limit on the size of arguments to
       the exec functions.  This limit could be as low as 4096 bytes including the  size  of
       the  environment.   For scripts to be portable, they must not rely on a larger value.
       However, I know  of  no  implementation  whose  actual  limit  is  that  small.   The
       --show-limits  option  can be used to discover the actual limits in force on the cur‐
       rent system.

BUGS
       It is not possible for xargs to be used securely, since there will always be  a  time
       gap  between  the production of the list of input files and their use in the commands
       that xargs issues.  If other users have access to the system, they can manipulate the
       filesystem  during this time window to force the action of the commands xargs runs to
       apply to files that you didn't intend.  For a more detailed discussion  of  this  and
       related  problems,  please  refer  to  the ``Security Considerations'' chapter in the
       findutils Texinfo documentation.  The -execdir option of find can often be used as  a
       more secure alternative.

       When  you  use  the  -I option, each line read from the input is buffered internally.
       This means that there is an upper limit on the length of input line that  xargs  will
       accept when used with the -I option.  To work around this limitation, you can use the
       -s option to increase the amount of buffer space that xargs uses, and  you  can  also
       use  an  extra  invocation of xargs to ensure that very long lines do not occur.  For
       example:

       somecommand | xargs -s 50000 echo | xargs -I '{}' -s 100000 rm '{}'

       Here, the first invocation of xargs has no input line length limit because it doesn't
       use  the  -i  option.   The second invocation of xargs does have such a limit, but we
       have ensured that it never encounters a line which is  longer  than  it  can  handle.
       This  is  not  an  ideal  solution.   Instead, the -i option should not impose a line
       length limit, which is why this discussion appears in the BUGS section.  The  problem
       doesn't occur with the output of find(1) because it emits just one filename per line.

REPORTING BUGS
       GNU findutils online help: <https://www.gnu.org/software/findutils/#get-help>
       Report any translation bugs to <https://translationproject.org/team/>

       Report any other issue via the form at the GNU Savannah bug tracker:
              <https://savannah.gnu.org/bugs/?group=findutils>
       General  topics  about  the  GNU findutils package are discussed at the bug-findutils
       mailing list:
              <https://lists.gnu.org/mailman/listinfo/bug-findutils>

COPYRIGHT
       Copyright ? 1990-2021 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version
       3 or later <https://gnu.org/licenses/gpl.html>.
       This  is free software: you are free to change and redistribute it.  There is NO WAR‐
       RANTY, to the extent permitted by law.

SEE ALSO
       find(1), kill(1), locate(1), updatedb(1), fork(2), execvp(3), locatedb(5), signal(7)

       Full documentation <https://www.gnu.org/software/findutils/xargs>
       or available locally via: info xargs

                                                                                    XARGS(1)

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